Melanoma is an increasingly common cancer and a major cause of cancer-related death. Metastatic melanoma has a low survival rate and few effective treatments, thus new targets are needed for effective therapy. A molecule implicated in metastasis of cancer in general is c-Met, a receptor tyrosine kinase (RTK) involved in cell proliferation, migration, and invasion. c-Met and its ligand, hepatocyte growth factor (HGF), may be upregulated in metastatic melanoma and are implicated in invasion and clinical disease progression. However, prior studies of c-Met and HGF in melanoma are limited in scope. Our preliminary data suggest that inhibition of HGF or c-Met may have promise for clinical application in melanoma. The novelty of our current proposal is the investigation of c-Met expression in a panel of human melanomas of varying genetic background, evaluation of the downstream signaling mechanism in the setting of BRAF and NRAS mutations, and preclinical studies of HGF and c-Met blockade in a mouse xenograft model of human melanoma. The significance of this proposal is that it may lead to clinical trials of novel personalized therapy of melanoma using agents currently available in early stage trials in other cancers. Pilot work on c-Met in our lab has revealed that c-Met is present and active in the majority of tested melanoma cell lines. In addition, we have found that inhibition of either HGF (with antibody) or c-Met (with small molecule inhibitors) inhibited proliferation of melanoma cells in vitro. We also linked this inhibition to deactivation of signaling pathways MAPKinase and mammalian target of rapamycin (mTOR). The proposed project aims to expand our understanding of c-Met expression and activation in melanoma cell lines as well as tissue samples. I hypothesize that, similar to the small number of cell lines previously tested, c-Met is active in the majority of melanoma cell lines and in human metastatic melanoma tissue specimens. Successful deactivation of c-Met after treatment with HGF antibody suggests that c-Met activation in melanoma is HGF dependent. I predict that as baseline c-Met activation increases, the effectiveness of blocking HGF and c-Met also increases, as measured by cell proliferation and migration. Blockade of c-Met activation will likely lead to reduced proliferation via deactivation of the MAPKinase and mTOR pathways, and will lead to reduced migration via deactivation of the Src/FAK pathway. Activating mutations of downstream molecules BRaf and NRas, common in melanoma, may alter effectiveness of c-Met blockade. To determine the effect of HGF and c-Met blockade in vivo, I will evaluate the effect of HGF and c-Met inhibition on human melanoma growth in a mouse model. Based on in vitro findings, I predict that HGF and c- Met blockade will inhibit tumor growth in a mouse xenograft model. I hypothesize that in vivo inhibition of proliferation is due to deactivation of the MAPKinase pathway. The proposed in vivo studies evaluate overall and end-organ toxicity of the two inhibitors studied, which will provide necessary preliminary data for eventual FDA approval. Transitioning the studies of c-Met blockade in melanoma from in vitro studies to animal studies is an important step in development of targeted therapies against c-Met for metastatic melanoma in humans.